This invention relates generally to rotary compressors, and more particularly, to a sealed rotary compressor housed in a separate pressure vessel which employs magnetic means to apply power to the rotors, and a substantially zero pressure differential is created across a separate gear housing from a rotor housing.
A rotary compressor such as a Root's blower (pump) is a multiple rotor positive displacement pump. Generally, a two-lobed blower is utilized wherein two rotors are rotatably mounted in a rotor housing and spin in opposite directions to trap gas therebetween and the outer walls of the housing. Trapped gas is moved from a low pressure port to a higher pressure port where it is displaced by the opposite rotor.
Conventional Root's blowers have suffered numerous limitations due to their high cost and tendency to introduce contaminants into the pumped gas.
In one design, the pumping chamber housing the rotors is separated from gears which are operatively associated with the rotors. These gears are housed in a distinct adjacent gear chamber. A rotor shaft supports a rotor and a gear in such a manner that the two are capable of rotational movement about the longitudinal axis of the shaft. Each shaft extends into the gear chamber, the pumping chamber, then to a powre source adapted to provide rotational movement of the shaft itself. As the shaft rotates, the rotor and gears are also caused to rotate. Disposed within the gear chamber is a lubricating solution such as oil which is provided to minimize damage to the gears due to wear.
A shaft seal is provided and disposed in an aperature of an end plate separating the two chamber. The shaft seal extends within the interior of the gear chamber and because there is a differential pressure between the two chamber, the seal must be a pressure seal. Should there be a failure in the pressure seal, the pressure differential causes lubricating fluid from the gear chamber to pass into the pumping chamber where contamination with the pumped gas (or pumped fluid) occurs. This pump also is disadvantageous because pumped gas has a tendency to leak.
The problems with a blower of this type are significantly magnified where the pump is utilized in a recirculating system such as found in laser applications. It is highly desirable for the pumped gas to have as little contamination as possible. When organic contaminants, such as those found in oil, are introduced into the gas and pumped into a laser system, deposits are formed on internal resonator surfaces and can greatly reduce the efficiency of the laser. Extensive clean-up may be required along with consequent maintenance.
Conventional Root's blowers not only have contamination problems because they are generally used for evacuation systems and often employ other systems such as traps to stop backstreaming. Leakage problems are also present in recirculating applications. These blowers have also required the use of a liquid lubricant in the gear chamber and a pressure differential is often created between the gear and pump housings. Numerous failures have been reported when lubricating material inadvertently enters the pumping chamber due to failed pressure seals.
Because this pressure differential exists, it has been necessary to have a shaft seal that is very tightly fit to the shaft. As the shaft rotates heat is generated and eventually the seal fails. Again the problem of contamination exists.
In many traditional Root's blowers there is pump chamber, and an evacuated chamber between the pump and gear chambers. A shaft extends through the various chambers requiring the employment of numerous shaft seals. Typically, dynamic seals are utilized and an oil bath is included. It is not unusual to have piston seals as part of the system. External pumping (another pump) is necessary to evacuate this intermediate chamber. With the employment of piston rings and seals which extend into the gear housing chamber, leakage occurs which ultimately results in contamination of the flowing gas.
Another disadvantage is the use of gears to transfer mechanical power between rotors in addition to a timing function. This prevents the use of lighter weight gears and/or lubricants and requires an oil bath. If the pump is in its own housing, a costly cast iron housing is necessary to prevent deformation under atmospheric pressure in order to limit the amount of back flow through the clearance gap.
There exists a need for an improved rotary compressor (Root's blower) which minimizes lubricating fluid contamination, and leakage of the pumped gas. Problems associated with conventional shaft seals (both internal and external) can create major problems with cleanliness and can be quite expensive. It would be highly desirable to have a compressor that did not have a intermediate chamber disposed between the gear chamber and the pumping chamber which requird a pumping down of the intermediate chamber. Additionally, it would be desirable to provide a compressor made of low cost materials, having compact design, and which would not require the gears to transfer mechanical power between the rotors. Inherent in this concept would be the ability to employ low cost pump chamber housing materials.